The present invention is directed towards a syringe having a retractable needle.
Syringes in which the needles are able to be retracted into the syringe barrel after use are known.
Such syringes have been developed in order to reduce the risk of needle-stick injuries experienced by health professionals. Typically these earlier syringes provide means by which the syringe piston can engage the needle base at the end of the injection procedure. The piston and needle can then be withdrawn into the barrel of the syringe by the user. A disadvantage of such syringes is that in the withdrawn position, the end of the plunger extends from the open barrel of the syringe. If the end of the plunger is accidentally depressed, the needle may be pushed out of the barrel. In order to avoid this occurring complicated locking arrangements for locking the plunger in the withdrawn position have been proposed. Typical locking arrangements have a twist-lock mechanism.
A further disadvantage of these syringes is that withdrawal of the plunger and needle into the syringe barrel and subsequent locking action is a two handed operation. Thus, the ultimate safety of the syringe is subject to the method of operation of the user. An error in operation may result in incomplete withdrawal of the needle into the barrel and/or failure to securely lock the needle within the barrel.
In order to overcome the disadvantages of the manually operable single use syringes, syringes which automatically withdraw the needle into the body of the plunger after fluid delivery have been developed.
Typically, the piston engages the base of the needle and is then withdrawn into the body of the piston. Withdrawal may be actuated by a spring or by air pressure in which case the body of the piston has an evacuated chamber.
For withdrawal of the needle and plunger to occur, the needle and plunger must be released from the syringe barrel and piston respectively. Further, the piston must be able to engage the base of the needle. There have been a number of different arrangements which have been proposed to provide the respective engagement and needle release means. Examples of such arrangements include rupturable membranes or frangible members which can fracture so as to release either the needle or the piston. Other arrangements include complex claw arrangements whereby claws are deformed at the end of the depression stroke of the plunger to either release and/or engage the respective parts.
A major disadvantage of these arrangements is that they are quite complicated and include a large number of parts. This makes the syringes complicated and expensive to manufacture. However, a particular disadvantage is that the mechanism must operate when the needle is inserted into the flesh of a patient In the above mechanisms, a reasonable amount of force is required to rupture or deform the various parts so as to activate the withdrawal mechanism. Such force may be greater than that normally required during a normal delivery stroke of the plunger. Any increase in downwards force on the plunger at the end of fluid delivery has potential to injure or inflict pain or discomfort to a patient. Also, the necessity to use additional force at the end of an injection may be undesirable during procedures such as spinal injections.
It is therefore an object of the invention to provide a syringe which may at least partially overcome the above disadvantages or provide the public with a choice.
According to a broad form of the invention there is provided a hypodermic syringe having;
a barrel with an open end, a base end and an internal bore;
a needle assembly including a needle base member located inside the bore and releasably engaged with the base end and a needle which protrudes through the base end of the barrel;
a plunger slidable within the bore. the plunger having a piston releasably engaged therewith and a chamber having air evacuated therefrom, the chamber being sealed at one end by the piston; wherein the piston includes means for engaging the needle base member such that in use when the plunger is depressed and the piston approaches the base end of the barrel, the piston can engage the needle base member, the needle base member is released from the base end and the piston is released from the plunger such that the piston, needle base member and needle can be forced into the chamber by atmospheric pressure, wherein the needle base member is releasably engaged with the base end of the barrel by means of a split ring movable from an engagement position to a release position.
The needle base member is releasably engaged to the base of the barrel by a split ring moveable from an engagement to a release position. Typically, the split ring Is located between opposing recesses in the needle base member or the base of the barrel, thereby locking the two components together. Typically either the base member or recess has a second recess, deeper than the first recess spaced from the first recess in the direction of plunger travel. Typically, the second and first recesses are connected to form a stepped recess.
In use, the split ring can be moved such that It expands or contracts into the second recess (depending upon whether it is on the barrel or the needle base member) thereby releasing the needle base member from engagement with the barrel.
The syringe of the present invention includes a plunger releasably attached to a piston. The piston has an evacuated chamber which is sealed at one end by the piston. The piston is releasably engaged with the plunger. The plunger may be engaged by any suitable means which will allow the piston to be released from the plunger when the piston meets the needle base at the termination of the plunger stroke.
Preferably, the piston Is also releasably engaged to the plunger by a split ring. Preferably, the plunger further includes means for locking the plunger to the base end of the barrel when the plunger is fully depressed. This locking mechanism locks the plunger inside the barrel and prevents withdrawal of the plunger and also re-use of the syringe. The locking mechanism may include any suitable arrangement and may include one or more projections or recesses located on the plunger or barrel and one or more complimentary recesses or projections located on the other of the barrel or plunger. The locking mechanism preferably includes a split ring. The split ring may be the same split ring which releasably engages the plunger and piston. In this case, upon release of the piston, the split ring can engage an inwardly facing locking projection located on the base and of the barrel.
According to a further embodiment of the present invention, there is provided a hypodermic syringe having;
a barrel with an open end, a base end and an internal bore and a locking means at the base end;
a needle assembly including a needle base member located inside the bore and releasably engaged with the base end and a needle which protrudes through the base end of the barrel;
a plunger slidable within the bore, a piston releasably engaged with the plunger and a chamber having air evacuated therefrom, the chamber being sealed at one end by the piston; wherein the piston includes means for engaging the needle base member such that in use, when the plunger is depressed and the piston approaches the base end of the barrel, the piston engages the needle base member, the needle base member is released from the base end, the plunger releases the piston and is simultaneously engaged by the locking means at the base end of the barrel; such that the piston, needle base member and needle are forced into the chamber by atmospheric pressure and the plunger remains engaged with the barrel means so that it may not be removed from the bore.
In either embodiment, the piston is released from the plunger, the difference in air pressure forces the plunger back inside the evacuated chamber. Typically, there is a seal between the piston and chamber walls such that the piston can be retained inside the chamber by atmospheric pressure. Typically the barrel may include one or more air inlets at the base end. These air inlets facilitate withdrawal of the piston into the chamber.